1. Field of the Invention
The present invention generally relates to a vehicle driving force control apparatus in which at least one wheel from among the front and rear wheels is driven by an internal combustion engine. More specifically, the present invention relates to a drive control apparatus that is useful in a four-wheel drive vehicle in which one pair of wheels from among the front wheels and rear wheels is driven by an internal combustion engine and the other pair of wheels is driven by an electric motor.
2. Background Information
Four-wheel drive control apparatuses in which one pair of wheels from among the front wheels and rear wheels is driven by an engine and the other pair of wheels is driven by an electric motor are disclosed in Japanese Laid-Open Patent Publication Nos. 7-231508 and 8-300965.
In the drive control apparatus presented in Japanese Laid-Open Patent Publication No. 7-231508, the engine drives a generator and the electric energy generated by the generator drives the electric motor. The drive control apparatus controls the electric energy supplied from the generator to the electric motor based on the condition of the vehicle. As a result, a large capacity battery is not necessary, and thus, the weight of the vehicle can be reduced.
In the drive control apparatus presented in Japanese Laid-Open Patent Publication No. 8-300965, an engine drives one pair of wheels and an electric motor drives the other pair of wheels. The electric motor is driven by electric energy from a battery. The drive control apparatus estimates the road surface friction coefficient xcexc. When the estimated road surface friction coefficient xcexc is low, the drive control apparatus controls the electric motor to an output torque based on the detected road surface friction coefficient xcexc. In short, the drive control apparatus attempts to prevent acceleration slippage of the wheels driven by the engine by adjusting the output torque of the electric motor in accordance with the detected road surface friction coefficient xcexc.
In view of the above, there exists a need for an improved vehicle driving force control apparatus that optimises the acceleration performance of the vehicle while also improving the fuel consumption and other energy efficiencies. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that in the apparatus described in Japanese Laid-Open Patent Publication No. 7-231508, the acceleration slippage of the wheels driven by the engine cannot be directly suppressed. Specifically, acceleration cannot be directly suppressed slippage because the four-wheel drive is accomplished by driving the electric motor based on the deviation of the front wheel rotational speed and the rear wheel rotational speed from a standard rotational speed that corresponds to the accelerator position and the deviation between the front wheel rotational speed and the rear wheel rotational speed.
Meanwhile, in the apparatus described in Japanese Laid-Open Patent Publication No. 8-300965, the electric motor is driven and the motor torque is controlled only under certain conditions. Specifically, the electric motor is driven and the motor torque is controlled only when the brakes are not being operated, the gear shift is in a position other than neutral, the accelerator is being depressed, the vehicle is travelling at or below a prescribed speed, and the road surface friction coefficient xcexc is equal to or below a prescribed value. However, acceleration slippage of the wheels driven by the engine cannot be directly suppressed.
In short, in both of these drive control apparatuses, there is the possibility that, in situations where the accelerator is excessively depressed, the wheels driven by the engine will experience more acceleration slippage than necessary and sufficient acceleration performance and travelling stability will not be attainable.
The present invention focuses on this kind of problem and aims to provide a vehicle driving force control apparatus that optimises the acceleration performance of the vehicle while also improving the fuel consumption and other energy efficiencies.
The present invention can be basically carried out by providing for a vehicle having front and rear wheels with at least one of the front and rear wheels being a drive wheel driven by an internal combustion engine that drives a generator. The driving force control apparatus basically comprises a drive wheel slippage estimating section, and a generator control section. The drive wheel slippage estimating section is configured to estimate if acceleration slippage is occurring in the main drive wheels. The generator control section is configured to control a generation load torque of the generator to substantially correspond to an acceleration slippage magnitude of the main drive wheels, when the drive wheel slippage estimating section estimates acceleration slippage occurring in the main drive wheels.
With the present invention, the portion of the output torque from the internal combustion engine that is surplus torque corresponding to the magnitude of the acceleration slippage of the driving wheels, i.e., corresponding to the torque that cannot be used effectively by the drive wheels, is converted to electric energy. Therefore, the acceleration slippage of the drive wheels driven by the power of the internal combustion engine is suppressed and the necessary acceleration performance can be obtained in such situations as when the vehicle is starting to move.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.